1. Field of the Invention
The invention relates to a communications system, more particularly to a receiver of a communications system and to an auto-gain control method of the receiver.
2. Description of the Related Art
The development of communications systems with high bit transmission rates is inevitable to cope with the explosion of digital information. Although there currently exists a 10 Gbase-Fiber (IEEE 802.3ae) standard, the use of fiber optics as a transmission medium does not meet requirements for low cost transmission. Therefore, a 10Gbase-T (IEEE 802.3an) standard was proposed, which uses a twisted-pair copper wire as a transmission medium in order to promote and make popular the establishment of ultra-high speed Ethernet systems.
Referring to FIG. 1, in a conventional network transmission environment, each transceiver pair 1 comprises a receiver 2 and a transmitter 3. In general, the receiver 2 comprises components, such as an analog front end (AFE) unit, an analog-to-digital converter (ADC), a crosstalk suppressing unit, an equalizer, etc. The analog front end unit comprises an analog auto gain controller (AAGC). When establishing a connection, the receiver 2 will first determine signal power of the transmitter 3 before determining an optimum analog gain level of the analog auto gain controller.
In general, it is only after the analog gain level has been determined that the receiver 2 converges coefficients of the crosstalk suppressing unit, a feed forward equalizer and a feedback equalizer. Therefore, when the signal power of a far end or near end transmitter 3 changes, the analog gain level of the analog auto gain controller of the receiver 2 changes accordingly, such that the coefficients of the crosstalk suppressing unit, the feed forward equalizer and the feedback equalizer must be converged anew. Taking a 10 Gbase-T Ethernet network that complies with the IEEE 802.3an standard as an example, frequent adjustment of the signal power of the transmitter 3 is necessary when establishing a connection so as to avoid excessive signal power that can result in crosstalk with other receivers 2. Re-converging of coefficients can easily lead to disconnection and re-connection problems.
Therefore, in order to make the process of establishing a connection smoother, there is a need to dispense with re-converging of the coefficients of the receiver 2 whenever the signal power of the transmitter 3 is adjusted during connection establishment.